Organic Chemistry

Janice Gorzynski Smith

Chapter 31

Synthetic Polymers

Educators

AS
SK
CV

Problem 1

Give the shorthand structures of poly(vinyl chloride) and nylon 6,6 in Section 31.1.

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Problem 2

What polymer is formed by chain-growth polymerization of each monomer?

Ian K.
Numerade Educator

Problem 3

What polymer is formed by the radical polymerization of each monomer?

a. CH$_2$ = C(CH$_3$)CO$_2$CH$_3$
b. CH$_2$ = C(CH$_3$)CN

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Problem 4

Draw the mechanism for the radical polymerization of vinyl acetate (CH$_2$ = CHOCOCH$_3$) using (CH$_3$)$_3$CO- OC(CH$_3$)$_3$ as the initiator.

Ian K.
Numerade Educator

Problem 5

Explain why radical polymerization of styrene forms branched chains with 4$^\circ$ carbons as in $\textbf{A}$, but none with 3$^\circ$ carbons as in $\textbf{B}$.

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Problem 6

Explain why cationic polymerization is an effective method of polymerizing CH$_2$ = C(CH$_3$)$_2$ but not CH$_2$=CH$_2$.

Ian K.
Numerade Educator

Problem 7

Which method of ionic polymerization-cationic or anionic-is preferred for each monomer? Explain your choices.

a. CH$_2$= C(CH$_3$)COOCH$_3$
b. CH$_2$= CHCH$_3$
c. CH$_2$= CHOC(CH$_3$)$_3$
d. CH$_2$= CHCOCH$_3$

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Problem 8

Draw a stepwise mechanism for the conversion of acrylonitrile (CH$_2 =$ CHC $\equiv$ N) to polyacrylonitrile, $-$ [CH$_2$CHC $\equiv$ N]$_n$ - , using butyllithium (BuLi) as the initiator and CO$_2$ as the electrophile to terminate the chain.

Ian K.
Numerade Educator

Problem 9

Explain why styrene (CH$_2$ = CHPh) can be polymerized to polystyrene by all three methods of
chain-growth polymerization.

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Problem 10

Draw the alternating copolymer formed from each set of monomers.

a. CH$_2$ = CHPh and CH$_2$ = CHCN
b. F$_2$C = CFCF$_3$ and CH$_2$ = CF$_2$

Ian K.
Numerade Educator

Problem 11

Draw the mechanism for the radical copolymerization of CH$_2$ = CHCH = CH$_2$ and CH$_2$ = CHPh to form styrene-butadiene rubber, $-$ [CH$_2$CH = CHCH$_2$CH$_2$CHPh]$_n -$ .

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Problem 12

What polymer is formed by anionic polymerization of each monomer?

Ian K.
Numerade Educator

Problem 13

Assign the $E$ or $Z$ configuration to the double bonds in neoprene. Draw a stereoisomer of neoprene in which all the double bonds have the opposite configuration.

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Problem 14

The polymerization of CH$_2$ = CHCH = CH$_2$ under radical conditions affords products $\textbf{A}$ and $\textbf{B}$. Draw a mechanism that accounts for their formation.

Ian K.
Numerade Educator

Problem 15

What polyamide is formed from each monomer or pair of monomers?

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Problem 16

Polyethylene terephthalate is also prepared by the transesterification of dimethyl terephthalate with
ethylene glycol. Draw the mechanism for this nucleophilic acyl substitution.

Ian K.
Numerade Educator

Problem 17

The first synthetic fibers were prepared by the step-growth polymerization of HOOC(CH$_2$)$_4$COOH and HOCH$_2$CH$_2$OH. Draw the structure of this polymer and suggest reasons why it is less suitable than either nylon 6,6 or PET for use in consumer products.

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Problem 18

Lexan can also be prepared by the acid-catalyzed reaction of diphenyl carbonate with bisphenol A.
Draw a stepwise mechanism for this process.

Ian K.
Numerade Educator

Problem 19

(a) Draw the structure of the prepolymer $\textbf{A}$ formed from 1,4-dihydroxybenzene and excess
epichlorohydrin. (b) Draw the structure of the cross-linked polymer $\textbf{B}$ formed when $\textbf{A}$ is treated with H$_2$NCH$_2$CH$_2$CH$_2$NH$_2$ as the hardening agent.

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Problem 20

Draw a stepwise mechanism for Step [2) in Figure 31.7 using AlCl$_3$ as the Lewis acid catalyst.

Ian K.
Numerade Educator

Problem 21

Thermosetting resins similar to Bakelite (Section 31.7) have also been prepared from renewable
feedstocks. One method uses cardinal, the major constituent of the liquid obtained from roasted
cashew nutshells. What polymer is obtained when cardinal is treated with formaldehyde (H$_2$C = O) in the presence of a proton source?

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Problem 22

Why can't chemical recycling$-$that is, the conversion of polymer to monomers and re-conversion
of monomers to polymer$-$be done easily with HDPE and LDPE?

Ian K.
Numerade Educator

Problem 23

Organic polymers can also be incinerated as a means of disposal. (a) What products are formed
on combustion of polyethylene? (b) What products are formed on combustion of polyethylene
terephthalate? (c) Are these reactions exothermic or endothermic? (See Sections 6.4 and 30.3 for
related reactions.) (d) Propose a reason why HDPE and PET must be separated from poly(vinyl
chloride) prior to incineration.

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Problem 24

What polymers are formed from each monomer?

Ian K.
Numerade Educator

Problem 25

Draw the structure of the polymer formed by chain-growth polymerization of each monomer.

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Problem 26

What monomer{s) are used to prepare each polymer or copolymer?

Ian K.
Numerade Educator

Problem 27

Draw the structure of the polymer formed by step-growth polymerization of each monomer or pair of monomers.

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Problem 28

Draw the structure of the polymer formed by chain-growth polymerization of each monomer.

Ian K.
Numerade Educator

Problem 29

Draw the structure of the alternating copolymer formed from each pair of monomers.

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Problem 30

What monomer(s) are used to prepare each polymer or copolymer?

Ian K.
Numerade Educator

Problem 31

Draw each polymer in Problem 31.30 using the shorthand representation shown in Figure 31.2.

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Problem 32

Draw a short segment of each polymer: (a) isotactic poly(vinyl chloride); (b) syndiotactic polyacrylonitrile; (c) atactic polystyrene.

Ian K.
Numerade Educator

Problem 33

Draw the structure of the polymer that results from anionic polymerization of $p$-trichloromethylstyrene (CCl$_3$C$_6$H$_4$CH = CH$_2$) using ethylene oxide as the electrophile to terminate the chain.

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Problem 34

Draw the structure of the polymer formed by step-growth polymerization of each monomer or pair of monomers.

Ian K.
Numerade Educator

Problem 35

$\textbf{ABS}$, a widely produced copolymer used for high-impact applications like car bumpers and crash helmets, is formed from three monomers$-$acrylonitrile (CH$_2 =$ CHCN), 1,3-butadiene (CH$_2$ $=$ CH $-$ CH $=$ CH$_2$), and styrene (CH$_2 =$ CH Ph). Draw a possible structure for ABS.

AS
Angela S.
Numerade Educator

Problem 36

Draw the structures of $\textbf{Quiana}$ and $\textbf{Nomex}$, two commercially available step-growth polymers formed from the given monomers. Nomex is a strong polymer used in aircraft tires and microwave transformers. Quiana has been used to make wrinkle-resistant fabrics.

Ian K.
Numerade Educator

Problem 37

Kevlar (Section 31.6A) is a very stiff polymer because its backbone contains many aromatic rings and its polymer chains are extensively hydrogen bonded to each other. Draw a short segment of two Kevlar chains, and indicate how the chains are hydrogen bonded to each other.

SK
Stefan K.
Numerade Educator

Problem 38

Explain the differences observed in the T$_g$ and T$_m$ values for each pair of polymers: (a) polyester $\textbf{A}$ and PET; (b) polyester $\textbf{A}$ and nylon 6,6. (c) How would you expect the T$_m$ value for Kevlar (Section 31 .6A) to compare with the T$_m$ value for nylon 6,6? Explain your prediction.

Ian K.
Numerade Educator

Problem 39

Explain why diester $\textbf{A}$ is now often used as a plasticizer in place of dibutyl phthalate.

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Problem 40

Draw a stepwise mechanism for the polymerization of isoprene to gutta-percha using (CH$_3$)$_3$CO$-$OC(CH$_3$)$_3$ as the initiator.

Ian K.
Numerade Educator

Problem 41

Cationic polymerization of 3-phenylpropene (CH$_2 =$ CHCH$_2$Ph) affords $\textbf{A}$ as the major product rather than $\textbf{A}$. Draw a stepwise mechanism to account for this observation.

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Problem 42

Explain why acrylonitrile (CH$_2 =$ CHCN) undergoes cationic polymerization more slowly than 3-butenenitrile (CH$_2 =$ CHCH$_2$CN).

Ian K.
Numerade Educator

Problem 43

Draw a stepwise mechanism for the anionic polymerization of styrene (CH$_2 =$ CHPh) to form polystyrene $-$[CH$_2$CHPh]$_n -$ using Buli as the initiator. Use CO$_2$ as the electrophile that terminates the chain mechanism.

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Problem 44

Although styrene undergoes both cationic and anionic polymerization equally well, one method is often preferred with substituted styrenes. Which method is preferred with each compound? Explain.

Ian K.
Numerade Educator

Problem 45

Rank the following compounds in order of increasing ability to undergo anionic chain-growth polymerization.

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Problem 46

In the presence of H$_3$O$^+$, 2-methylpropene oxide undergoes chain-growth polymerization such that nucleophilic attack occurs at the more substituted end of the epoxide. Draw a stepwise mechanism for this process, and explain this regioselectivity.

Ian K.
Numerade Educator

Problem 47

Draw a stepwise mechanism for the conversion of dihalide $\textbf{A}$ and 1,4-cyclohexanediol to polyether $\textbf{B}$ in the presence of AlCl$_3$.

CV
Corbyn V.
Numerade Educator

Problem 48

Draw a stepwise mechanism for the following reaction, which is used to prepare bisphenol A (BPA), a widely used monomer in polymer synthesis.

Ian K.
Numerade Educator

Problem 49

Draw a stepwise mechanism for the reaction of an alcohol with an isocyanate to form a urethane.

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Problem 50

Draw the products of each reaction.

Ian K.
Numerade Educator

Problem 51

Explain why aqueous NaOH solution can be stored indefinitely in polyethylene bottles, but spilling aqueous base on a polyester shirt or nylon stockings quickly makes a hole.

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Problem 52

What epoxy resin is formed by the following reaction sequence?

Ian K.
Numerade Educator

Problem 53

(a) Explain why poly(vinyl alcohol) cannot be prepared by the radical polymerization of vinyl alcohol (CH$_2 =$ CHOH). (b) Devise a stepwise synthesis of poly(vinyl alcohol) from vinyl acetate (CH$_2 =$ CHOCOCH$_3$). (c) How can poly(vinyl alcohol) be converted to poly(vinyl butyral), a polymer used in windshield safety glass?

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Problem 54

Although 1,3-propanediol (HOCH$_2$CH$_2$CH$_2$OH) can now be prepared from carbohydrate feedstocks (Section 31.8), it can also be prepared from petroleum feedstocks. Devise a synthesis of HOCH$_2$CH$_2$CH$_2$OH from CH$_3$CH $=$ CH$_2$, a product of petroleum refining.

Ian K.
Numerade Educator

Problem 55

Devise a synthesis of terephthalic acid and ethylene glycol, the two monomers needed for polyethylene terephthalate synthesis, from the given starting materials.

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Problem 56

The reaction of $p$-cresol with CH$_2 =$ O resembles the reaction of phenol (PhOH) with CH$_2 =$ O, except that the resulting polymer is thermoplastic but not thermosetting. Draw the structure of the polymer formed, and explain why the properties of these two polymers are so different.

Ian K.
Numerade Educator

Problem 57

In addition to glycolic and lactic acids (Section 31 .6B), dissolving sutures can also be prepared from each of the following lactone monomers. Draw the structure of the polymer formed from each monomer.

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Problem 58

Compound $\textbf{A}$ is a novel poly(ester amide) copolymer that can be used as a bioabsorbable coating for the controlled release of drugs. $\textbf{A}$ is a copolymer of four monomers, two of which are amino acids or amino acid derivatives. The body's enzymes recognize the naturally occurring amino acids in the polymer backbone, allowing for controlled enzymatic breakdown of the polymer and steady release of an encapsulated drug. Identify the four monomers used to synthesize $\textbf{A}$; then use Figure 29.2 to name the two amino acids.

Ian K.
Numerade Educator

Problem 59

Researchers at Rutgers University have developed biocompatible polymers that degrade into nonsteroidal anti-inflammatory drugs. For example, the reaction of two equivalents of benzyl salicylate and one equivalent of sebacoyl chloride forms a poly(anhydride ester) called PolyAspirin, which hydrolyzes to salicylic acid (an anti-inflammatory agent) and sebacic acid, which is excreted. This technology can perhaps be used for localized drug delivery at specific sites of injury. What is the structure of Poly Aspirin?

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Problem 60

Mel mac, a thermosetting polymer formed from melamine and formaldehyde (CH$_2 =$ O), is used to make dishes and countertops. Draw a stepwise mechanism for the condensation of one mole of formaldehyde with two moles of melamine, which begins the synthesis of Melmac.

Ian K.
Numerade Educator

Problem 61

Although chain branching in radical polymerizations can occur by intermolecular H abstraction as shown in Mechanism 31.2, chain branching can also occur by intramolecular H abstraction to form branched polyethylene that contains butyl groups as branches.

a. Draw a stepwise mechanism that illustrates which H must be intramolecularly abstracted to form butyl substituents.
b. Suggest a reason why the abstraction of this H is more facile than the abstraction of other H's.

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Problem 62

The reaction of urea [(NH$_2$)$_2$C = O] and formaldehyde (CH$_2 =$ O) forms a highly cross-linked polymer used in foams. Suggest a structure for this polymer. [$Hint$: Examine the structures of Bakelite (Figure 31.7) and Melmac (Problem 31.60).]

Ian K.
Numerade Educator